1. Field of the Invention
The present invention relates to a warm air furnace, and to be more specific, relates to a warm air furnace enabling fuel consumption conserving operation.
2. Description of the Related Art
For example, in a gas fan heater which is a warm air furnace, a gas burner and an air blow fan are equipped inside a body case, in which the heater operation is carried out by elevating the room temperature by drawing in the indoor air by the rotational operation of the air blow fan, and blowing the air heated by the gas burner into the room. Generally, the warm air furnace includes a temperature adjustment function, and a combustion amount at the gas burner and an air blow amount of the air blow fan are adjusted so that a target temperature set by the user using a temperature setting switch approximately coincide with the actual room temperature detected by a room temperature sensor provided in the vicinity of an air inlet of the indoor air.
With the rise in the environmental consciousness of the user and from the purpose of reduction in heating cost, the warm air furnace is required to conduct heater operation while conserving fuel consumption. As one type of such warm air furnace, there is known a warm air furnace equipped with a saving operation function (also known as a fuel consumption conserving operation function) (for example, refer to Japanese Patent Application Laid-Open No. H8-189708). In this type of warm air furnace, the target temperature is decreased slightly, accompanying a lapse of time after the room temperature reaches the target temperature. To be more specific, there is a type in which the target temperature is decreased by 1° C. after a lapse of 30 minutes from the time when the room temperature reaches the target temperature, and the target temperature is further decreased by 1° C. after a lapse of further 30 minutes. The sensory temperature of the user does not change greatly, even when the target temperature is decreased slightly as is described above. Therefore, by conducting the saving operation, it is possible to reduce the combustion amount of the gas burner, and obtain fuel consumption conserving effect without making the user feel uncomfortable.
Apart from the warm air furnace in which the target temperature is decreased each time by a predetermined temperature, there is a warm air furnace in which a decreasing amount of the target temperature is varied in accordance to the magnitude of the heating load, for example the decreasing amount of the target temperature during the saving operation is varied in accordance with the room temperature at the commencement of the heating operation and the increasing amount of the room temperature after commencement of heating operation.
On the other hand, there is known a warm air furnace equipped with a moderate operation function (also known as on/off operation function). This is a function for assisting the temperature adjustment function, by interrupting the combustion operation of the gas burner in the case where the temperature detected by the room temperature sensor continues to increase even when the combustion amount of the gas burner is decreased to its minimum, so as to prevent excessive heating and to make the room temperature approximately coincide with the target temperature. To be more specific, when the room temperature becomes higher than the target temperature by a predetermined temperature or more, the combustion operation of the gas burner is stopped, and thereafter combustion operation of the gas burner is resumed when the room temperature decreases to a heating resume temperature set near the target temperature.
Further, there is known a warm air furnace enabling simultaneous use of the saving operation and the moderate operation (refer to Japanese Patent Application Laid-Open No. H11-23064). This type of warm air furnace is equipped with two switches enabling setting of the on/off of the saving operation function and the moderate operation function independently from each other, and the user is free to select and set the on/off of each function.
However, there are cases where the fuel consumption conserving effect cannot be obtained even when the saving operation or the moderate operation is carried out, depending on the situation such as a heating load. That is, even though the saving operation is carried out, in the case where the heating load is smaller than the heating capacity of the gas burner in the minimum combustion amount, the fuel consumption conserving effect is not sufficient because it is not possible to decrease the heating capacity any more. On the other hand, even though the moderate operation is carried out, when the room temperature becomes higher than the set temperature, the combustion operation of the gas burner is not interrupted in the case where the heating load is larger than the heating capacity of the gas burner in the minimum combustion amount, the fuel consumption conserving effect is not sufficient. Further, it is difficult for the general user to set appropriate operating function in accordance with the situation such as the heating load.